The causes and consequences of decline in muscle biomechanical quality with aging are unknown. Since it has been postulated that a large portion of age-related loss of mobility and disability with aging is linked with loss of muscle strength, identification of such causes is essential in order to develop therapeutic strategies that may effectively preserve physical disability with aging. This project entails a number of studies that scan a wide range of hypotheses concerning the origin of muscle quality and its consequence with aging. This discovery stage will be followed by more in dept studies that focus on the most promising lines of research.